1. Technical Field
The present disclosure relates generally to aerosol analyzers and other particle measuring instruments, and more specifically to a particle capture device usable in aerosol analyzers and other particle measuring instruments.
2. Background Information
Fine atmospheric aerosols resulting from internal combustion engines, fossil fuel fired power plants, painting/stripping faculties, gas discharge boiler operations and other anthropogenic and biogenic sources, are known to have a serious impact on climate and human health. These aerosols are comprised of micron and sub micron sized particles, having various size distributions and chemical compositions. Such particles can influence climate directly by scattering or absorbing sunlight, and indirectly by altering cloud coverage. Further, such particles can contribute to health problems such as asthma, lung cancer, cardiovascular disease, respiratory disease, and other conditions. Given their impact on climate and human health, fine atmospheric aerosols composed of micron and sub micron sized particles are the subject to widespread study and monitoring.
A variety of different types of aerosol analyzers and other particle measuring instruments have been developed to determine particle size distributions and chemical compositions of fine atmospheric aerosols. In one type of instrument, a focused particle beam is generated and directed towards a generally flat collection surface. The particles impact the collection surface, and a portion of them are retained. The retained particles are vaporized, and the resulting gaseous molecules are provided to a detector that produces results. While such an instrument may provide valuable information, typical designs have shortcomings.
One shortcoming of typical designs is that they have low particle collection efficiency. A significant percentage of particles impacting the collection surface may simply bounce off (i.e. impact and rebound), and be lost rather than vaporized and analyzed. Low particle collection efficiency may limit the overall performance of the instrument. While attempts have been made to increase particle collection efficiency, such attempts have had mixed results.
Some attempts have focused on changing particle properties to reduce particle bounce. Modifications are made to the particles before they impact the collection surface. Other attempts have focused on modifying the impact surface, such as using greased plate impactors. However, particle bounce is a complex phenomenon. A wide variety of factors, including size, chemical composition, phase (e.g., liquid or solid), impact velocity, and the like, may be in play. Given the complexities, modifying particle or impact surface properties to reduce particle bounce is challenging.
Other attempts have focused on applying corrections to compensate for low particle collection efficiency. Empirically determined correction factors may be applied to results to compensate for losses of mass or losses of concentration resulting from particle bounce. However, determining the appropriate correction factors may be challenging. Further, correction factors merely mask, and do not address, the underlying problem of low particle collection efficiency.
Accordingly, there is a need for improved techniques that may be used to, among other things, improve particle collection efficiency in aerosol analyzers and other particle measuring instruments.